In the related art, electric motors with brushes have been used as wiper motors for an automobile. In this type of electric motor, a plurality of permanent magnets are arranged at equal intervals in the circumferential direction on the inner peripheral surface of a cylindrical yoke, and an armature is surrounded by these permanent magnets and rotatably supported by the yoke. The armature has an armature core, and a plurality of teeth is formed in a radial fashion on the armature core. Slots are spaces that are formed between the respective teeth. Electric coils are wound so as to surround the plurality of teeth through two slots. The armature has a rotary shaft, and a commutator is fixed to the rotary shaft.
The commutator includes an insulating body formed in a columnar shape, and segments including a plurality of metal pieces. The plurality of segments are insulated from each other and disposed side by side along the circumferential direction on the insulating body. A winding starting end and a winding finishing end of an electric coil are connected to each of these segments. A brush comes into sliding contact with each segment, and an electric current is supplied to each electric coil via the segment from this brush. A magnetic field passing through the armature core is generated by the electric current supplied to the electric coil, and the armature is rotated together with the rotary shaft by a magnetic attractive force or repulsive force that is generated between the permanent magnets fixed to the yoke and the armature core.
In recent years, demands for miniaturization and high performance of the wiper motors are increasing. As a result, there is known a wiper motor that includes magnets of which the number of magnetic poles is four (the number of pole pairs is two), an armature with more teeth, and four brushes and that enables changes in rotational speed (for example, refer to Patent Document 1). In the motor disclosed in this Patent Document 1, patterns of energization to the four brushes are changed, and each mode of a low-speed rotation mode, a medium-speed rotation mode, and a high-speed rotation mode is selected. This motor includes the armature with four magnetic poles and a number of teeth, and the rotating speed of the armature is variable.